1. Field of the Invention
This invention relates to methods for severing tube sheets to expose the bores of hollow fiber embedded thereon.
2. Prior Art
In making a certain type of membrane gas separator the end of a bundle of hollow fiber membranes is positioned in a cylindrical mold and a liquid casting resin is poured into the mold and cured to a solid state. The purpose of the casting is to serve as a tube sheet when the fiber bundle is placed in a cylindrical shell. In order to remove gases which permeate to the bores of the fibers it is necessary to transversely sever the tube sheet to expose the fiber bores. A major problem with this is that almost every type of cutting process results in smearing the relatively soft fibers and closing the bores thereof. Various attempts have been made to avoid this problem.
U.S. Pat. No. 4,183,283 discloses that a tube sheet can be severed in any suitable manner and then a thin layer of the tube sheet is removed by using a knife blade to scrape the severed face of the tube sheet to open the bores of hollow fibers embedded in the tube sheet.
U.S. Pat. No. 4,271,740 discloses apparatus for cutting a tube sheet having a fiber bundle embedded therein, the apparatus being provided with a pair of blades positioned at different angles.
U.S. Pat. No. 4,369,605 discloses the opening of bores in a cast tube sheet by severing the tube sheet and then grit-blasting the severed face of the tube sheet to open the fiber bores.
U.S. Pat. No. 3,503,288 discloses a method for cutting hollow plastic filaments embedded in a solid plastic matrix to expose the bores of the filaments wherein the end of the tube sheet is brought into contact with a cutter and is then rotated such that the cutter trims the end of the tube sheet. This patent states that attempts have been made to fracture a tube sheet by the use of a controlled bending force or a shaped explosive charge. The patent further states that, when an attempt is made to fracture a tube sheet larger than two inches in diameter, the resultant fracture is erratic, difficult to predict and usually damages beyond repair the integrity of the seal between the cast wall, hollow filaments and the casing in which the tube sheet is mounted.